Prior art suspension systems have been provided for vehicles to isolate the vehicle frame, or chassis, from impacts and vibrations resulting from vehicle wheels traversing uneven terrain. Vehicle ride characteristics have complex dynamics characterized by nonlinearities, vehicle roll and pitch, vehicle flexibility effects, varying parameters, unknown friction, dead zones and high amplitude disturbances. Excess vibration results in artificial vehicle speed limitations, reduced vehicle-frame life, biological effects on passengers and detrimental consequences to cargo. Present suspension systems traditionally use passive suspension systems which can only offer a compromise between the two conflicting criteria of comfort and performance by providing spring and dampening coefficients of fixed rates. Passive suspension systems have been provided by separate coil springs and shock absorbing dampers, in which power is not input by a controlled power source to counteract impacts and vibrations resulting from traversing the rough terrain. The traditional engineering practice of designing spring and dampening functions as two separate functions has been a compromise from its inception in the late 1800's. As a result, vehicles have always been designed, styled and built around the space-weight requirements and performance limitations of traditional suspension configurations.
To provide increased mobility and stability, independent passive suspensions have been developed which have proven their worth in improved mobility over rough courses, but high wheel travel has sacrificed improved stability. Active suspension systems provide a solution for improved stability, as well has providing improved mobility. Active suspension systems reduce these undesirable ride characteristics by providing active, powered components which isolate the car body from tire vibrations induced by uneven terrain, to provide improved comfort, road handling performance and safety for a variety of terrains and vehicle maneuvers. In active vehicle suspension systems, actuators are provided to actively apply forces which counteract and balance forces applied to the chassis of the vehicle.
Off-road capable military vehicles provide special demands upon suspension systems. In battle conditions, to enhance survivability vehicles are often required to move at high speeds over rough terrain. As such speeds, damage to the vehicle and riders in a vehicle may occur due to jouncing of the vehicle, in addition to loss of stability leading to vehicle roll-over. Suspension ride characteristics over rough terrain is also complicated by differences between laden and unladen weights of the vehicles becoming so broad that traditional suspension systems are unable to span the load range effectively, causing serious degradation in performance of the vehicle ride quality, load handling and control.
Mobile firing platforms, such as military tanks, vehicles to which cannons and missile launchers are mounted, and such, add the additional constraint that vehicle suspensions be capable of locking at a particular ride height to provide the ability to accurately aim weapons mounted on the platform. After weapons producing large recoil are fired, it is desirable that vehicle suspensions quickly absorb the recoil and associated vibrations so that the weapons may be fired more rapidly than if the suspensions took longer times to absorb the recoil vibration. For motorized, mobile weapons systems, such as military tanks, it is desirable that the suspension may be quickly locked, stabilized after firing, and then unlocked again to allow maneuverability over rough terrain between firing locations.